The present invention relates generally to high-frequency amplifiers. More particularly, the present invention has found specific advantageous application in circuit amplification environments where circuits are sensitive to voltage excursions at input ports thereof. A particular example application of the present invention is directed to variable gain amplifier (xe2x80x9cVGAxe2x80x9d) circuits where benefit is realized in achieving a large dynamic range, a wide frequency response and/or improved linearity, while consuming relatively low amounts of power.
The electronics industry continues to strive for high-powered, high-functioning circuits. Significant achievements in this regard have been realized through the fabrication of very large-scale integration of circuits on small areas of silicon wafer. For applications directed to high-frequency communications, main objectives in the design and manufacturing of such devices are typically directed to obtaining circuitry that occupies as small an area and uses the smallest amount of power as practicable, while at the same time preserving the integrity of the data being communicated by the signal.
One circuit often used in communications circuitry is commonly referred to as a variable gain amplifier (xe2x80x9cVGAxe2x80x9d). VGAs are used in numerous electronic products such as global positioning (GPS) receivers, wireless local area networks and mobile communication devices, such as cordless and cellular phones. In particular, VGAs are used in various parts of such devices, for example, in the radio frequency (RF), intermediate frequency (IF) and the low frequency, and/or in connection with base-band signal processing for these devices.
A typical VGA includes a differential pair of transistors, which steers a portion of an input current signal to an output terminal, while the other unused portion of the input current signal is directed to ground. The amount of signal current that is steered to the output terminal depends on the differential control voltage that is applied to the respective bases of the differential pair of transistors. In general, applying a higher control voltage to the base of one of the transistors, as compared to the base of the other transistor, will determine the extent to which the input signal current is available at the output terminal. The formula for the gain control characteristic of such a VGA circuit is determined as a function of translinear equations defined by the particular arrangement of the circuitry. For details of this analysis, reference may be made to various sources including, for example, the text by B. Gilbert, entitled Current-Mode Circuits from a Translinear Viewpoint: a Tutorial, at Chapter 2 (United Kingdom 1990) and U.S. Pat. Nos. 5,999,053, 6,028,478 and 5,994,961.
In attempting to design a VGA for a particular application, consideration is typically given to several known limitations of typical VGA circuit arrangements. Using wireless communications as an example category of applications, these limitations are often directed to controlling the signal level at the input or output of a functional block. Controlling this signal level is often realized by changing the gain or attenuation in a circuit via a control voltage. In VGA circuits, however, such control voltage adjustments can result in serious operational shortcomings including, for example, limitations in the dynamic range and significant increases in power consumption. Variations of signal level with control voltage adjustments can also result in the degradation of key operational aspects used in characterizing a VGA; namely, noise and nonlinearity performance.
Accordingly, there is a need to provide a variable gain amplifier having an expanded dynamic range, a wide frequency response and/or improved linearity, while consuming relatively low amounts of power.
The present invention is implemented in various embodiments directed to addressing the above applications and concerns, as well as other advantages that will become apparent upon a careful review of the following discussion. For example, certain aspects of the invention are directed to advantages discovered in connection with stacking current-steering circuits in combination with eliminating voltage excursions from a signal presented to the stacked current-steering circuits. Appropriately implemented, this approach can result in a number advantages relating to improvements in terms of dynamic range, linearity and power consumption.
According to a particular example application, the present invention is embodied in the form of first and second current-steering sections arranged to gain-adjust (or xe2x80x9camplify,xe2x80x9d including both positive and negative gain-adjustments) a differential current input signal. Each of the first and second current-steering sections is current driven via differential current paths. The first current-steering section configured and arranged to source current and thereby drive the second current-steering section.
Another aspect of the invention employs stacked Gilbert cells, as referred to in connection with the above background discussion, to form a variable gain amplifier (xe2x80x9cVGAxe2x80x9d) circuit that achieves a large dynamic range, a wide frequency response and improved linearity, while consuming relatively low amounts of power. In this context a Gilbert cell is a form of a transistor-based amplifier in which current at an input port is divided (or separated), according the transistor-based amplifier design, into at least two outputs.
In yet another specific example embodiment of the present invention, an amplification arrangement includes a voltage to current converter for current feeding the above-characterized VGA circuit.
The above summary is not intended to provide an overview of all aspects of the present invention. Other aspects of the present invention are exemplified and described in connection with the detailed description.